I live near Baltimore and have a 400+sf family room that I hoped to heat with electric radiant heat. It is an addition with a crawl space under it. Subfloor is wood and has insulation under it. Rest of the house is heat pump wt gas backup. I work from home and like the idea of the radiant floor for the day when I'm here instead of using the whole system. We have solar though not much extra in the winter but would cover it in the fall/spring I think. Floor is hardwood (that could use a refinish). Question for if I go ahead? Any way to figure out how much electricity it will draw to keep it warm during winter? What kind of floor is ideal - do I need to replace the hardwood with tile - if so can I add a rug? How much do you think this will cost? Is this a good idea?

Consider sealing and insulating the crawl space (remove underfloor insulation) and then running some/all heat from your current system (assuming hot air) into the crawl space. Electricity needed will be much less than electric radiant heat. And no need to rip up the floor. Yet still radiant heat with a warm floor.

Well IF you want to shutdown the main system and only run a standalone system for the smaller space you will need to know how much you will need and how much resistance to it's loss you have(insulation).

What is the R value of the ceiling, wall and floor insulation? how large are the windows and what is their R value? How much of the wall is on the outside and how much into the rest of the house. What is the outside temp and what is the temp in the rest of the house. What temperature is it now and what temperature do you want it to be? Heat transfers because of differences in temperature. Once you know the r values and areas There is a series of calculations that can be done once you know these things, but you will have to figure each different insulated barrier and each different temperature difference separetaly and then total them all up. It is a bit of basic math, but once you break the different surfaces and their areas down, it is pretty straightforward. I just described how to do these basit calcs in a recent basement thread.

In general, electric resistance heat is not the most cost effective, unless you only need just a little bit of it, then it's convenient applications usually outweigh the added costs.

I don't think you are going to be able to add electric radiant without pulling up the hardwood.

Have you looked into a small mini-split? It would of course have to be sized properly based on the demand, but this sounds like a good application for one of those unless you have your heart set on radiant floor. Then perhaps a staple-up hot water system might be the least intrusive...

Very useful info! Looks like I have a lot of homework to do . I looked into a mini-split system and have priced that but have not priced the radiant idea, which was in a room I once stayed in and felt great to me. I was trying to do homework before getting that pricing. I don't mind spending more up front but don't want it to be much less efficient than the mini-split. I see that there are a lot of factors and do not think I can figure out R values etc. I know only that I want it around 67 degrees during the day and can find average temps around here. Is there someone I can hire to give an assessment of these things and help me compare. Already had a couple hvac people here to price a mini-split system but they didn't know about that. Would it be an energy-efficiecy company? And who do I call to price a radiant elec system for that room- is it a flooring company. Wish I have some DYI skills - I am only good at decoration and finish work :( Thanks Again!

jonr's recommendation that you insulate and over-condition the crawl space to raise the floor temp has merit, and is probably cheaper than many other solutions. (Insulating the crawlspace has merit on it's own terms, even without the radiant floor.) Depending on the actual heat load a mini-split heating the insulated crawlspace to 80-85F may work just fine.

The only way to get it up to mini-split efficiency is with air source heat pumps. There is at least one smaller modulating reversible chiller out there that may not be ridiculously oversized or ridicululously overpriced.

http://www.chiltrix.com/small-chiller-home.html

It's going to be way overkill for just one 400 square foot room, but it's operating cost would be comparable to a mini-split if done well. (A big "if"...)

But getting to the right solution always starts with a careful heat load calculation.

Thanks! I'll look into that. I have just arranged for someone to come and assess the insulation side of it.

There is no substitute for radiant floors. You do not have to, nor is it advisable, pull up the wood flooring. As Dana suggests, the first step is a proper heat load to determine how much heat you need. Then the sources can be considered. The space and the climate indicate small loads and thus a low return on investment for high tech, low comfort solutions.

I would insulate the crawl space as suggested and make sure free air from the basement is allowed to flow to the crawl space. If this does not improve comfort consider a sub-floor, low voltage electric system. There really is no reason to have home if you can't be comfortable in it.